The FBI has warned U.S. retailers to prepare for more cyber attacks after discovering about 20 hacking cases in the past year that involved the same kind of malicious software used against Target Corp. in the holiday shopping season. The U.S. Federal Bureau of Investigation distributed a confidential, three-page report to retail companies describing the risks posed by "memory-parsing" malware that infects point-of-sale systems, which include cash registers and credit-card swiping machines found in store checkout aisles. more